Thought I wld draw attention to a recent paper-

Quarterly Journal of the Royal Meteorological Society - 2005 papers
Vol. 131 OCTOBER 2005 Part B No. 612
JOHN D. LOCATELLI, MARK T. STOELINGA and PETER V. HOBBS - Re-examination of
the split cold front ion the British Isles cyclone of 17 July 1980 3167
The authors revisit a case study by Browning and Roberts,using the MM5
model, and draw comparisions with landfalling fronts on the NW seaboard of
America.Unfortunately I can't find the papers freely online ATM,but they ask
the final question-

"......why split fronts appear to be more common in the British Isles than
in the Pacific Northest.........."

BTWThis is one last papers by Peter Hobbs (a British expatriot trained at
Imperial ) who died last year.

http://cargsun2.atmos.washington.edu/
http://improve.atmos.washington.edu/


--
regards,
David

add '17' to Waghorne to reply

"Waghorn" wrote in
:

"......why split fronts appear to be more common in the British Isles
than in the Pacific Northest.........."

Do they mean split as in a kata-front or split as in ana- towards the
trailing end of the cold front and kata- towards the low pressure end of
the front?

Cheers
Richard

"Richard Dixon" wrote in message
...
"Waghorn" wrote in
:

"......why split fronts appear to be more common in the British Isles
than in the Pacific Northest.........."

Do they mean split as in a kata-front or split as in ana- towards the
trailing end of the cold front and kata- towards the low pressure end of
the front?

Cheers
Richard

A split cold front is where the upper part of the front overruns the lower. The
top part then has the main rain area, the rear part becomes the surface cold
front (where the surface airmass changes), and the bit in between is called the
shallow moist zone characterized by low cloud and drizzle but may also become
potentially unstable as dry air aloft moves over the top. Most cold fronts in
summer over the UK are split. Ana and kata refer to how the wind direction
component perpendicular to the front varies with height. If it decreases with
height the front is ana, if it increases it is kata, hence split cold fronts are
usually kata fronts, but don't confuse ana and kata with weak or strong a kata
front can still give a lot of rain.

HTH

Will.
--


" Ah yet another day to enjoy "
-------------------------------------------------------------------------------
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
-------------------------------------------------------------------------------

"Richard Dixon"
"......why split fronts appear to be more common in the British Isles
than in the Pacific Northwest.........."

Do they mean split as in a kata-front or split as in ana- towards the
trailing end of the cold front and kata- towards the low pressure end of
the front?

Cheers
Richard

No Rich they're refering to a cross section through the frontal zone where
lower theta air aloft overruns the surface frontal zone (in the case study
not far equatorward of the triple point), as outlined by Will.But of course
there is a spectrum, from which Browning extracted his
archetype(s).Different terminologies are around-eg. the term cold front
aloft is used in the States-I think mostly for such fronts east of the
Rockies.

I was wondering if somebody might have an opinion on a reply to the
question, even whether it's a real phenomenon (in the paper a suggestion is
made that the observation maybe due to selection in research strategies ),


--
regards,
David

add '17' to Waghorne to reply

"Waghorn" wrote in message
...

"Richard Dixon"
"......why split fronts appear to be more common in the British Isles
than in the Pacific Northwest.........."


I was wondering if somebody might have an opinion on a reply to the
question, even whether it's a real phenomenon (in the paper a suggestion is
made that the observation maybe due to selection in research strategies ),

It sounds to me to be similar to the effect of a breaking wave on the sea
shore.

The difference then, between the North Pacific and North Atlantic air flows,
would be the relief of the American and European land masses. The reason
for more split fronts in the British Isles would be the height of the
mountains
here. Perhaps an average height of 3000 feet is that needed to induce split
fronts, and the Rockies are too high.

Alternatively, perhaps the lower relief in Ireland and the higher relief in
Scotland causes a tipping effect which rolls the split northwards. This
idea is easy to confirm if the split does start when the front reaches
Ireland,
and works its way north as the front moves eastward. If the splits are on
fronts
that reach Scotland first, then perhaps it is just mountains rising 3 to 4
thousand
feet that induce them.

How does that fit with the facts?

Cheers, Alastair.

"Alastair McDonald"
"Waghorn" "......why split fronts appear to be more common in the
British Isles
than in the Pacific Northwest.........."

It sounds to me to be similar to the effect of a breaking wave on the sea
shore.
.......................................


How does that fit with the facts?

Cheers, Alastair.


Er,nice start, but...........no, if I read you right ;-).
Over the ocean basins 'splitting ' can't be induced by orography except in
the sense of it's dependence on the lower stratospheric/upper troposphere
dynamics ultimately related to downstream effects tied to the Rockies (in
the Atlantic basin).However it may well relate to this 'breaking' of Rossby
waves and the effect on maturing baroclinic waves late in their lifecycle,
ie at the end of the stormtrack.
All ideas welcome though.Split fronts are often remarked upon in this
group,and it's interesting there may still be open questions.I can't find a
recent climatology of frontal types tho some work was done in the UK in the
'50s,


--
regards,
David

add '17' to Waghorne to reply

"Waghorn" wrote in message
...

"Alastair McDonald"
"Waghorn" "......why split fronts appear to be more common in the
British Isles
than in the Pacific Northwest.........."

It sounds to me to be similar to the effect of a breaking wave on the sea
shore.
.......................................


How does that fit with the facts?

Cheers, Alastair.


Er,nice start, but...........no, if I read you right ;-).

I don't think you have, but it is probably my fault.

Over the ocean basins 'splitting ' can't be induced by orography except in
the sense of it's dependence on the lower stratospheric/upper troposphere
dynamics ultimately related to downstream effects tied to the Rockies (in
the Atlantic basin).However it may well relate to this 'breaking' of Rossby
waves and the effect on maturing baroclinic waves late in their lifecycle,
ie at the end of the stormtrack.

I am assuming that the splitting happens when the fronts reach Britain,
not in the Open Atlantic. Thus, just as sea waves increase and break
as they reach the shore due to the shelving sea bed, so too the air
on leaving a flat ocean and moving onto a shelving topography
will also form waves which break. In general they will be invisible,
since they are covered by more air rather than being an obvious
difference in phase which happens with liquid waves breaking in
a gaseous atmosphere.

But it may be possible to see them by observing the behaviour of
clouds, although I am not sure what they would look like. Presumably
the cloud would be carried higher, just as sea wave gets higher. But
this analogy may be unnecessary.

At what height does the split happen at? If is more than 3000 feet
and less than the average height of the Rockies? It may be that
the bottom of the front is stalled by the mountains whereas the
split, being above the British mountain tops, is unimpeded and
flows onwards.

The other scheme I suggested is that when the front hits the
wedge shaped topography of Britain side on, it is imparted
will a roll, which creates the split effect. What is really needed,
to see whether that roll is possible, is a wind tunnel with a
wedge across the direction of flow, but with its sharp end
of the wedge pointing slightly upwind.

I am actually providing two solutions to the problem here. They
can't both be wrong!

Cheers, Alastair.

"Alastair McDonald"
.................................................. ......................
I am actually providing two solutions to the problem here. They
can't both be wrong!

Cheers, Alastair.


Unfortunately I think they are in this case-as splitting starts over the
open ocean.
When fronts interact with topography damming of the cold air can occur at
low levels and decouple from the flow aloft-but that is a different
phenomenon.
We're talking about an effect to due to the dynamics of the lower
stratosphere and upper to mid troposphere.
Unfortunately the analogy with breaking ocean waves only goes so far.
Overrunning of the dry air is particularly apparent in WV imagery,but is
also apparent in IR and VIS.
I'll try to find some references when I have the time later,

--
regards,
David

add '17' to Waghorne to reply

"Waghorn" wrote in message
...

"Alastair McDonald"
.................................................. .....................
I am actually providing two solutions to the problem here. They
can't both be wrong!

Cheers, Alastair.


Unfortunately I think they are in this case-as splitting starts over the
open ocean.

Oh well, third time lucky. Look at it this way; you have a prevailing
south westerly flow over the British Isles. Thus the air mass first
hits Kerry in the south west of Ireland where it has to rise a few
hundred feet. As it travels further north eastwards, it eventually
reaches Fort William where Ben Nevis takes it to over 4000 feet.
Now if that air mass was a stunt motor car with its right wheels
being raised by a factor of ten (huh?) then it too would probably
roll over into the Atlantic, just as the air mass does! Or does it
roll the other way :-?

Cheers, Alastair.
..

"Alastair McDonald" Unfortunately I think they are in this case-as
splitting starts over the
open ocean.

Oh well, third time lucky. Look at it this way; you have a prevailing
south westerly flow over the British Isles. Thus the air mass first
hits Kerry in the south west of Ireland where it has to rise a few
hundred feet. As it travels further north eastwards, it eventually
reaches Fort William where Ben Nevis takes it to over 4000 feet.
Now if that air mass was a stunt motor car with its right wheels
being raised by a factor of ten (huh?) then it too would probably
roll over into the Atlantic, just as the air mass does! Or does it
roll the other way :-?

Cheers, Alastair.

Now you've totally lost, not for the first time.;-)
Breaking waves -yes,stunt cars -no.Have a look at-
http://ams.allenpress.com/amsonline/...S%3E2.0.CO%3B2

http://makeashorterlink.com/?W21F52CAC
Weather and Forecasting: Vol. 1, No. 1, pp. 23–41.
Conceptual Models of Precipitation Systems
Keith A. Browning

Imagery from radars and satellites is one of the main ingredients of
nowcasting. When used to provide very detailed forecasts of precipitation
for a few hours ahead, the imagery needs to be interpreted carefully in
terms of synoptic and mesoscale phenomena and their mechanisms. This paper
gives an overview of some conceptual models that are useful for this
purpose. The models represent a variety of systems associated with
midlatitude cyclones and also mesoscale convective systems in the tropics
and midlatitudes. Specific phenomena discussed are
warm conveyor belts, including those with rearward- and forward-sloping
ascent in ana and kata cold frontal situations, respectively;
.................................................. .................................................. .................................................. ........................................

--
regards,
David

add '17' to Waghorne to reply